The present invention relates to a pattern formation method for use in fabrication of semiconductor integrated circuit devices and the like, and more particularly, it relates to a method for forming a resist pattern by selectively irradiating a resist film of a positive chemically amplified resist material with electron beams or extreme UV of a wavelength of a 1 nm through 30 nm band.
In accordance with recently increased degrees of density and integration of semiconductor integrated circuits, the wavelength of exposing light used in photolithography has been more and more shortened. Recently, extreme UV (of a wavelength of a 300 nm band or shorter) and krF excimer laser (of a wavelength of a 248 nm band) are practically used, and ArF excimer laser (of a wavelength of a 193 nm band) will be put to practical use in the near future. However, these exposing light cannot be used in very fine processing with a design rule of 100 nm or less because of their disadvantage of resolution performance.
Therefore, photolithography using, as exposing light applicable to very fine processing, F2 laser (of a wavelength of a 157 nm band) or electron beam is now under examination, but a resist material suitable to F2 laser or electron beams has not been found yet.
As a resist material for electron beams, a resist composition with a principal chain to be cut (as one disclosed in, for example, Japanese Laid-Open Patent Publication No. 1-163738) is used for forming a mask or the like. However, this resist material cannot be used in very fine processing for fabrication of semiconductor devices because its sensitivity and resolution are too low.
In order to overcome these disadvantages, examination is being made on and a large number of papers have been presented on a chemically amplified resist material using a catalytic function of an acid generated through irradiation with energy beams. However, such a resist material still has a large number of problems to overcome before being put to practical use.
For example, Japanese Laid-Open Patent Publication Nos. 7-209868, 11-305440, 2000-66401 and the like disclose a resist material including a combination of poly(hydroxystyrene/styrene/tert-butyl acrylate) and triphenylsulfonium trifluoromethanesulfonate, and Japanese Laid-Open Patent Publication Nos. 7-261377, 8-179500 and the like disclose a resist material including a combination of a mixed polymer of poly(p-hydroxystyrene/styrene/tert-butyl acrylate) and poly(p-hydroxystyrene/tert-butyl acrylate) and triphenylsulfonium trifluoromethanesulfonate. In these resist materials, however, trifluoromethanesulfonic acid generated through irradiation with energy beams has high volatility and easily moves. Therefore, under conditions where a high vacuum state is kept for a long time as in the use of electron beams, the acid volatilizes or moves during time from exposure to annealing, and hence, a very fine pattern cannot be satisfactorily formed.
For example, Japanese Laid-Open Patent Publication No. 2000-66382 and the like disclose a resist material including a combination of poly(p-hydroxystyrene/styrene/tert-butyl acrylate) and triphenylsulfonium p-toluenesulfonate. However, the degree of acidity of p-toluenesufonic acid generated through irradiation with energy beams is too low to attain sufficient sensitivity for practical use.
For example, Japanese Laid-Open Patent Publication No. 8-146610 and the like disclose a resist material including a combination of poly(p-hydroxystyrene/tert-amyl methacrylate) and triphenylsulfonium trifluoromethanesulfonate, and J. Photopolym. Sci. Technol., 1997, Vol. 10 (No. 3), pp. 397-408 by H. Ito et al., J. Photopolym. Sci. Technol., 1996, Vol. 9(No. 4), pp. 557-572 by H. Ito et al., Japanese Laid-Open Patent Publication Nos. 7-261377 and 8-179500 and the like disclose a resist material including a combination of poly(p-hydroxystyrene/tert-butyl acrylate) and triphenylsulfonium trifluoromethanesulfonate. However, due to the volatility and mobility of trifluoromethanesulfonic acid generated through irradiation with energy beams, a very fine pattern cannot be satisfactorily formed by using any of these resist materials. Also, even when a pattern is formed, the dry etching resistance of these polymer is too low for practical use.
For example, Japanese Laid-Open Patent Publication No. 11-305440 and the like disclose a resist material including a combination of poly(hydroxystyrene/styrene/tert-butyl acrylate) and triphenylsulfonium perfluorobutanesulfonate, and Japanese Laid-Open Patent Publication No. 2000-66382 and the like disclose a resist material including a combination of poly(p-hydroxystyrene/styrene/tert-butyl acrylate) and triphenylsulfonium perfluorobutanesulfonate. However, the degree of acidity of perfluoroalkanesulfonic acid such as perfluorobutanesulfonic acid generated through irradiation with energy beam is too low, and hence, the sensitivity is too low and the dissolution inhibiting property is too strong. Therefore, a pattern cannot be formed in a good shape by using any of these resist materials.
For example, Japanese Laid-Open Patent Publication No. 7-209868 and the like disclose a resist material including a combination of poly(hydroxystyrene)/styrene/tert-butyl acrylate) and N-(trifluoromethylsulfonyloxy)bicyclo-[2,2,1]-hept-5-en-2,3-dicarboxyimide. Also, ACS. Symp Ser., 1995, Vol. 614 (Microelectronics Technology), pp. 21-34 by H Ito to et al., J. Photopolym. Sci. Technol., 1996, Vol. 9 (No. 4)., pp. 557-572 by H. Ito et al. and the like disclose a resist material including a combination of poly(p-hydroxystyrene/tert-butyl actylate) and N-camphorsulfonyloxynaphthalimide of N-trifluoromethanesulfonyloxy-5-norbornene-2,3-dicarboxyimide. However, trifluoromethanesulfonic acid used in these resist materials has the same disadvantage as that described above, and hence, these resist materials cannot be used in very fine processing. Also, the degree of acidity of camphorsulfonic acid is too low to attain sufficient sensitivity of the resist material.
For example, Japanese Laid-Open Patent Publication No. 11-167200, European Patent Publication No. 813113 and the like disclose a resist material including a combination of poly(p-hydroxystyrene/styrene/tert-butyl acrylate) and di-(4-tert-butylphenyl)iodonium iodoniumcamphorsulfonate, Japanese Laid-Open Patent Publication No. 11-305441 and the like disclose a resist material including a combination of poly(hydroxystyrene/styrene/tert-butyl acrylate) and di-(4-tert-butylphenyl)iodoniumperfluorobutanesulfonate, and Japanese Laid-Open Patent Publication No. 2000-89453 and the like disclosure a resist material including a combination of poly(hydroxystyrene/tert-butyl actylate) and di-(4-tert-butylphenyl)iodoniumcamphorsulfonate. However, since iodonium salt is used in these resist materials, the dissolution inhibiting property is too low to attain high contrast and the sensitivity and the resolution are insufficient. Therefore, these resist materials cannot be used in very fine processing.
For example, Japanese Laid-Open Patent Publication No. 2000-187330 and the like disclose a resist material including a combination of poly(p-1-tert-butoxyethoxystyrene/p-hydroxystyrene) and 4-butoxyphenyldiphenylsulfonium 4-trifluoromethylbenzenesulfonate, Japanese Laid-Open Patent Publication No. 9-160246 and the like disclosure a resist material including a combination of poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/p-tert-butoxystyrene) and diphenyl-4-tert-butoxyphenylsulfonium p-toluenesulfonate, and Japanese Laid-Open Publication No. 9-211866 and the like disclose a resist material including a combination of poly(p-1-methoxypropoxystyrene/p-hydroxystyrene/p-tert-butoxycarbonyloxystyrene) and tris (4-tert-butoxyphenyl)sulfonium trifluoromethanesulfonate. However, a polymer having a non-cyclic acetal group as a protecting group cannot be formed into a desired pattern shape because electron beams are fluctuated due to a gas generated through decomposition during beam irradiation (what is called the outgassing), and the side face of the pattern is severely roughened. Also, in the case where trifluoromethanesulfonic acid is generated, the degree of volatility is so high that an insoluble skin layer is formed, and hence, a pattern cannot be formed.
For example, Japanese Laid-Open Patent Publication Nos. 7-261377, 8-179500 and 2000-187330 and the like disclose a resist material including a combination of poly(p-tert-butoxycarbonylmethoxystyrene/p-hydroxystyrene) and triphenylsulfonium trifluoromethanesulfonate. However, a very fine pattern cannot be satisfactorily formed by using this resist material due to the volatility and mobility of trifluoromethanesulfonic acid generated through irradiation with energy beams.
For example, Japanese Laid-Open Patent Publication Nos. 9-160246, 9-211866, 11-344808, 2000-122296 and 2000-187330 and the like disclose a resist material including triphenylsulfonium pentafluorobenzenesulfonate, tris(tert-butylphenyl)sulfonium pentafluorobenzenesulfonate, tris (tert-butoxyphenyl)sulfonium pentafluorobenzenesulfonate, triphenylsulfonium 3-trifluoromethylbenzenesulfonate, bis(4-methylphenyl)phenylsulfonium, 3,5-bis(trifluoromethyl)benzenesulfonate or the like. However, all polymers to be used in combination with these compounds have a non-cyclic acetal group as a protecting group, and hence, the problems of the fluctuation of electron beams owing to the outgassing and the roughness on the side face of the pattern cannot be avoided.
As described above, a positive chemically amplified resist material used for irradiation under vacuum with exposing light of electron beams or extreme UV with a 1 nm through 30 nm wavelength band has the following significant problems. The degree of volatility of an acid generated through irradiation with energy beam is high and the acid easily moves; the dry etching resistance of a polymer to be used is insufficient; the adhesion to a substrate is poor; a desired pattern cannot be formed due to the fluctuation of beams caused during the irradiation with the energy beams by decomposition/elimination of a protecting group suspended in a polymer; and the degree of acidity of an acid generated through irradiation with energy beam is too low to attain sufficient sensitivity of the resist material.
In the case where a fine pattern is to be formed by using electron beams or extreme UV as the exposing light, if the resist film has a large thickness, the aspect ratio of the resultant resist pattern is very high. When the aspect ratio of the resist pattern is high, the resist pattern cannot keep its shape and hence partly collapses, namely, a problem of pattern collapse is caused.
Accordingly, the resist film should have a thickness of 250 nm or less. When the resist film has a thickness of 250 nm or less, the problem of pattern collapse is minimally caused and the resolution of the resist film can be improved.
However, when the thickness of the resist film is smaller than 250 nm, the solubility in an alkaline developer of the resist film is increased even in an unexposed portion, which reduces the contrast in the solubility (namely, the contrast between the solubility of an unexposed portion and the solubility of an exposed portion). As a result, the resolution is disadvantageously lowered.